Fish oils are a valuable source of n−3 polyunsaturated fatty acids (PUFAs), including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are highly beneficial for human nutrition. Extensive research has been carried out to develop and improve processes for enriching and separating such PUFAs, including lipase-based methods.
Lipases are well suited for use as catalysts in processes involving highly labile n−3 polyunsaturated fatty acids, such as EPA and DHA, occurring in marine oil. This is due to their ability to act at low temperatures, their neutral pH and their mildness in action, which helps keep to a minimum undesired side reactions such as cis-trans isomerisations, double-bond migrations, polymerisations, oxidations, etc. Thus, the utilization of lipases for the hydrolysis and various esterification and transesterification transformations of fatty acids in marine oil is already well documented.
For example, in WO 95/24459 a process is described for treating an oil composition containing triglycerides of saturated and unsaturated fatty acids to transesterification reaction conditions with ethanol in the presence of a lipase which preferentially catalyses the transesterification of the saturated and monounsaturated fatty acids, thus obtaining from marine oil sources concentrates containing more than 70% by weight of the PUFAs EPA and DHA in the form of glycerides.
WO 2004/043894 discloses a process where free fatty acids from fish oil are esterified with methanol or ethanol using a lipase that preferentially esterifies EPA over DHA to obtain a mixture from which can be separated a DHA enriched fraction, with DHA in the form of a free fatty acid, and an EPA enriched fraction, with EPA in the form of an ethyl or methyl ester.
Because of the complexity of marine raw materials, polyunsaturated fatty acid derivatives in highly purified form are not easily prepared by any single fractionation technique. Further improved methods would be appreciated to separate and purify more effectively desired PUFA components from complex lipid mixtures such as fish oils.